This invention is a further development in the side-cavity coupled accelerator art described by E. A. Knapp, B. C. Knapp and J. M. Potter in an article entitled "Standing Wave High Energy Linear Accelerator Structures", 39 Review of Scientific Instruments 979 (1968); and as further described in U.S. Pat. No. 3,546,524 to P. G. Stark. More specifically, the invention provides an improvement in the drive coupling for the interlaced arrangement of side-cavity coupled substructures as described in said related applications.